The present invention relates to handling of micron scale structures using micro-devices, and more particularly to a system and method for multi-axis controlled translation and rotation of microcomponents using electrothermal microactuators.
Extraordinary advances are being made in micromechanical device and microelectronic device technologies. Further, advances are being made in MicroElectroMechanical Systems (xe2x80x9cMEMSxe2x80x9d), which incorporate integrated micromechanical and microelectronic devices and components. The term xe2x80x9cmicrocomponentxe2x80x9d is used herein generically to encompass microelectronic components, micromechanical components, as well as MEMS components, each generally having at least one dimension in the range between approximately 0.1 micron and 1000 microns. Advances in microcomponent technology have resulted in an increasing number of microcomponent applications. For example, various microcomponents are fabricated and then assembled together. That is, post-fabrication assembly operations may be performed on microcomponents to form devices that may have greater utility.
Accordingly, a need often arises for performing handling tasks for assembling microcomponents. For example, a microcomponent may need to be translated from one position to another position, such that the microcomponent can be presented for assembly together with another microcomponent. As another example, a microcomponent may need to be rotated in some manner such that it is properly oriented for assembly together with another microcomponent. For micro-optical technologies it may be desired to provide controlled movement of a lens with respect to a light source, such as a laser emitter, to produce desired light emission patterns. Similarly, it may be desired to provide controlled movement of an optical fiber end in order to properly interface with a light source.
Because of the small size of microcomponents, handling them to perform such assembly-related tasks is often complex. Due to scaling effects, forces that are insignificant at the macro scale become dominant at the micro scale (and vice versa). For example, when parts to be handled are less than one millimeter in size, adhesive forces can be significant compared to gravitational forces. These adhesive forces arise primarily from surface tension, van der Waals, and electrostatic attractions and can be a fundamental limitation to handling of microcomponents. (See e.g., xe2x80x9cA survey of sticking effects for micro parts handling,xe2x80x9d by R. S. Fearing, Proc. IEEE/RSJ Int. Conf. on Intelligent Robots and Systems, Vol. 2, pp. 212-217, Pittsburgh, Aug. 5-9, 1995; xe2x80x9cHexsil tweezers for teleoperated microassembly,xe2x80x9d by C. G. Keller and R. T. Howe, IEEE Micro Electro Mechanical Systems Workshop, Nagoya, Japan, Jan. 26-30, pp. 72-77, 1997; and xe2x80x9cMicroassembly Technologies for MEMS,xe2x80x9d by Michael B. Cohn, Karl F. Bxc3x6hringer, J. Mark Noworolski, Angad Singh, Chris G. Keller, Ken Y. Goldberg, and Roger T. Howe, Proc. SPIE Micromachining and Microfabrication, pp. 216-230, 1998.)
Also, relatively precise movement (e.g., translational and/or rotational movement) of a microcomponent is often required to perform assembly operations. Consider, for example, that in some cases mishandling of a part resulting in misalignment of only a few microns may be unacceptable, as the microcomponent to which the part is to be coupled may be only tens of microns in total size, and the portion of the microcomponent that is to be engaged for coupling may be even smaller. Thus, microcomponents present particular difficulty in handling for performing assembly operations.
Traditionally, a high-precision, external robot is utilized for handling of microcomponents to perform assembly operations. For instance, a high-precision, external robot having three degrees of translational freedom (e.g., capable of translating along three orthogonal axes X, Y, and Z) and having three degrees of rotational freedom may be used for handling microcomponents to perform assembly operations. For example, PolyTec PI manufactures a five degree of freedom robotic system specifically designed for high precision assembly of fiber optic modules. However, such external robots are generally very expensive. Additionally, external robots typically perform microcomponent assembly in a serial manner, thereby increasing the amount of time required for manufacturing micro-devices. That is, such robots typically handle one microcomponent at a time, thereby requiring a serial process for assembling microcomponents together.
Accordingly, MEMS systems have been developed to provide translation of a specimen in particular directions. For example, micro-translation systems have been developed in which a microcomponent stage, upon which a specimen may be placed or mounted, is operatively coupled to an actuator to provide controlled movement of the stage and, accordingly, translation of the specimen. Multiple actuators may be disposed in such a micro-translation system to provide a configuration in which motion in multiple directions may be provided, such as along both the X and Y axes.
In the prior art, bimorph actuators or thermal bimorph actuators generally move laterally in a plane of motion of the actuator. Surface micro-machined polysilicon thermal actuators and arrays traditionally have a hot arm and a cold arm. The hot arm is typically thinner and therefore more resistive than the cold arm. When passing electric current through those two arms in series, the hot arm due to its higher resistance heats and expands more than the cold arm, causing the free end of the actuator to move in an arcing motion.
xe2x80x9cApplications for Surface-Micromachined Polysilicon Thermal Actuators and Arraysxe2x80x9d by Comtois and Bright, Sensors and Actuators A 58, pp. 19-25, 1997, and xe2x80x9cElectrothermal actuators fabricated in four-level planarized surface micromachined polycrystalline silicon,xe2x80x9d by Comtois et al., Sensors and Actuators A 70, pp. 23-31, 1998, describe thermal bimorph actuators having hot and cold arms, that provide motion only in a single direction along a single axis. xe2x80x9cAutomated Assembly of Flip-Up Micromirrors,xe2x80x9d by Reid et al., 1997 International Conference on Solid-State Sensors and Actuators, Chicago, pp. 347-330, June 1997, describes a xe2x80x9cback-bendingxe2x80x9d capability, such that the material of the hot arm reflows and shortens when pressed down towards a substrate at high temperature during the heating cycle, causing the actuator to bend in the opposite direction away from the substrate during a subsequent cooling cycle. U.S. Pat. No. 6,275,325/B1 (hereafter the ""325 patent) issued Aug. 14, 2001, describes an actuator that can move in one direction along one axis. Instead of thinning the hot arm to increase electrical resistance, the cold arm includes a metallic layer that reduces electrical resistance. Multiple actuators of this type are coupled to a stage, for example four actuators, which can then lift the stage along the Z axis and/or rotate it about any combination of the X and Y axes.
U.S. Pat. No. 5,909,078 (hereafter the ""078 patent), issued Jun. 1, 1999, describes various single direction thermal actuators known as thermal arch beam actuators.
U.S. Pat. No. 5,962,949 (hereafter the ""949 patent), issued Oct. 5, 1999, describes an apparatus that can produce XYZ motion in three orthogonal directions by cascading three thermal arch beam actuators. The ""949 patent describes two substantially identical single direction actuators independently driving a stage along the X and Y axes. A third actuator producing upward Z motion is embedded in the stage.
U.S. Pat. No. 5,870,007 (hereafter the ""007 patent), issued Feb. 9, 1999, describes a set of bimorph actuators that are coupled to a stage, which they can move in multiple directions. Each individual actuator has a xe2x80x9cmeander cantileverxe2x80x9d configuration and provides motion only in one direction. A single actuator is not capable of both in-plane and out-of-plane motion. To move the stage in multiple directions requires multiple actuators.
It is possible to design in-plane actuators that move in two directions. One prior art micro-translation system utilizes a plurality of thermal actuators (also referred to as heatuators) for in-plane translation. Directing attention to FIG. 1, micro-translation system 100 is shown including thermal actuators 110 and 120 directly coupled to stage 130 by flexures. Thermal actuators 110 and 120 are oriented to provide translation of stage 130, and components placed thereon, along both the X and Y axes. Specifically, thermal actuator 110 is coupled to stage 130 by flexure 131 and provides translation of stage 130 substantially along the X axis when hot-arm 111 is expanded by Joule heating and anchor 114, cold-arm 112, flexure 113, and anchor 115 cause transfer of lateral motion to flexure 131. Similarly, thermal actuator 120 is coupled to stage 130 by flexure 132 and provides translation of stage 130 substantially along the Y axis when hot-arm 121 is expanded by Joule heating and anchor 124, cold-arm 122, flexure 123, and anchor 125 cause transfer of lateral motion to flexure 132.
It should be appreciated, however, that micro-translation systems of the prior art utilizing thermal actuators in such a configuration suffer from several disadvantages. One such disadvantage is that the motion actively imparted by a given thermal actuator is generally unidirectional. Moreover, attempts to provide bi-directional motion using such micro-translation systems generally require substantial post-processing manufacturing steps, such as to electronically isolate the thermal actuators associated with different directions of motion, thereby making such systems difficult to implement. Additionally, the range of motion associated with the use of thermal bimorph actuators is limited to approximately 5 per cent of the overall length of the actuator. A further disadvantage is that translation of the micro-translation system stage along either axis is not independent of translation along the other axis. For example, translation of stage 130 provided by thermal actuator 120 along the Y axis will result in some translation of stage 130 along the X axis due to the torsional distortion of thermal actuator 120. This movement along the unselected axis is further aggravated due to the connection of connecting member 131 and thermal actuator 110 thereto.
Other known prior art micro-translation systems utilize indirect translation mechanisms. Directing attention to FIG. 2, micro-translation system 200 is shown utilizing indirect drive means. In the system of FIG. 2, a translation mechanism is disposed on each side of, and in the same plane with, stage 230 to controllably engage stage 230 and provide translation in a predetermined direction. Specifically, translation mechanism 210 includes actuator banks 211 and 212 coupled to lateral translation gear 231 by connecting arms 214 and 215, respectively. Similarly, translation mechanism 220 includes actuator banks 221 and 222 coupled to lateral translation gear 232 by connecting arms 224 and 225, respectively. Actuator banks 211, 212, 221, and 222 may comprise an array of thermal actuators, such as are shown in detail above in FIG. 1, and are oriented to provide translation of stage 230, and components placed thereon, along the X axis by causing lateral translation gears 231 and 232 to engage corresponding racks 233 and 234 using Y axis movement associated with actuator banks 211 and 221. Thereafter, movement along the X axis is provided by lateral movement of engaged translation gears 231 and 232 causing corresponding movement in racks 233 and 234, and thus stage 230, using X axis movement associated with actuator banks 212 and 222. Lateral translation gears 231 and 232 may then be disengaged from corresponding racks 233 and 234, again using Y axis movement associated with actuators 211 and 221, and re-engage with corresponding racks 233 and 234 at a different point, using X axis movement associated with actuators 212 and 222, for further movement of stage 230. An indirect thermal actuator drive mechanism similar to that of FIG. 2 is described in Reid et al. (1997), cited above.
Micro-translation systems of the prior art utilizing the above described indirect thermal actuator drive mechanisms suffer from several disadvantages. For example, although the range of motion is appreciably improved over that of the direct thermal actuator drive mechanism of FIG. 1, prior art configurations of such micro-translation systems provide translation of a stage along a single axis and, therefore, no prior art configuration has been proposed to provide movement along two axes which may be produced without substantial post-production manufacturing steps, i.e., no configuration is known in the prior art which may be produced using a monolithic manufacturing process.
Still other prior art micro-translation systems have implemented scratch drive actuators (SDAs) to provide translation of a stage. Directing attention to FIG. 3, one configuration of a SDA as is well known in the art is shown as SDA 310. Specifically, SDA 310 comprises plate 311, torsion mounts 312, and bushing 313. For operation, SDA 310 is disposed upon a substrate such that a conducting layer, such as conducting layer 322, is in juxtaposition with plate 311 and an insulating layer, such as insulating layer 321, is disposed therebetween.
Operation of SDA 310 is illustrated in FIGS. 4A-4C. Specifically, FIG. 4A shows voltage source 410 coupled to plate 311 and conducting layer 322 without any voltage applied thereto. However, as shown in FIG. 4B, a priming voltage may be provided by voltage source 410 and an electrostatic field associated therewith causes deflection of plate 311 such that its distal end is drawn toward conducting layer 322. As shown in FIG. 4C, the voltage provided by voltage source 410 may be increased to that of a stepping voltage such that plate 311 is more fully drawn toward conducting layer 322 causing bushing 313 to be displaced such that a distal end thereof steps forward distance xe2x80x9cSxe2x80x9d. Reducing the voltage provided by voltage source 410 to the priming voltage or below causes plate 311 to move forward distance xe2x80x9cSxe2x80x9d as bushing 313 is again righted, i.e., SDA 310 returns to an orientation as shown in FIG. 4A or 4B.
Although SDAs are generally useful in providing a relatively large range of linear motion, implementation of such actuators is still fraught with problems. For example, the use of such SDAs has generally required the use of a wire tether to provide activating potential to the SDA plate while accommodating the motion of the SDA. Moreover, although a bank of SDAs may be produced using a monolithic manufacturing process, all such SDAs have heretofore been electrically interconnected, causing all such SDAs in the bank to be activated simultaneously. Accordingly, in the prior art true independent bi-directional implementations of SDAs have not been provided using monolithic manufacturing processes, as the SDAs of each such direction have been electrically interconnected and thus operable only simultaneously. In order to provide SDAs which are independently operable in multiple directions, prior art implementations have required substantial post-processing manufacturing steps, such as to electronically isolate the SDAs associated with different directions of motion, thereby making such systems difficult to implement fully with monolithic production processes.
U.S. Pat. No. 5,072,288 (hereafter the ""288 patent), issued Dec. 10, 1991, describes microdynamic structures, including tweezers and actuators, that deflect along one or two axes by the application of electric potential differences to generate electrostatic forces. This technique, however, results in a limited range of motion and is dependent on the proximity of a deflecting beam to an electrically charged surface, which can be another deflecting beam. Additionally, instabilities in motion and deflection occur at short distances between the beam and the respective charged surface.
Accordingly, a need exists in the art for systems and methods to provide a relatively large range of stable motion in multiple directions with respect to a microcomponent. A need exists in the art for such multiple directions of motion to include bidirectional motion and/or motion along different (e.g., orthogonal) axes.
Moreover, a need exists in the art for systems and methods to provide a relatively large range of motion which may be produced using substantially monolithic manufacturing processes.
The present invention is directed to a system and method for providing independently controllable movement of microcomponents in a plurality of directions. In a microactuator having at least four substantially parallel longitudinal beams, each having a base end independently rigidly interconnected with a substrate, and a free end longitudinally opposite said base end, the free ends of all of the beams are detached from the substrate and rigidly interconnected with one another. By selectively thermally expanding at least one beam relative to the other beams, a bending moment is transmitted to the microactuator structure, causing controllable deflection of the free ends as a unit laterally away from the selectively thermally expanded beam(s). Depending on the choice of thermally expanded beam(s), the deflection can be in either of the intersecting lateral planes substantially parallel to the longitudinal beams.
In embodiments of the present invention, selective heating is achieved through a pair of beams by passing an electric current through them in series. Each beam has an independent electrical contact pad at the base end, and all beams are connected together electrically at the opposite free end. Selectivity is achieved by connecting a voltage across the pads of the selected beams and disconnecting the pads of the non-selected beams. In some embodiments, multiple microactuators are combined cooperatively, e.g., to move a stage in a plurality of directions.